1. Field of the Invention
The present invention relates to an electron source substrate, manufacturing method therefor, and image-forming apparatus using the electron source substrate.
2. Related Background Art
In recent years, flat, low-profile image-forming apparatuses have received a great deal of attention as image-forming apparatuses instead of large, heavy cathode ray tubes. As the flat image-forming apparatuses, liquid crystal displays have enthusiastically been studied and developed. However, the liquid crystal displays suffer dark images and narrow angles of field. The substitutes of the liquid crystal displays are emissive displays, i.e., plasma displays, vacuum fluorescent displays, and displays using emissive devices such as a surface conduction electron-emitting device. The emissive display can attain brighter images and wider angles of field than those of the liquid crystal display apparatus. On the other than, cathode ray tubes having a display of 30xe2x80x3 or more are being introduced, and are desired to realize larger displays. However, the cathode ray tube is not preferable because a larger one requires a larger space. As a bright, large-size display, the flat emissive display is suitable. The present inventors give attention to an image-forming apparatus using an electron-emitting device among flat emissive type image-forming apparatuses, and particularly to an image-forming apparatus using a surface conduction electron-emitting device capable of emitting electrons with a simple structure, which was proposed by M. I. Elinson et al. (Radio. Eng. Electron. Phys., 10, 1290 (1965)).
The surface conduction electron-emitting device emits electrons by flowing, in parallel with a film surface, a current through a small-area thin film formed on a substrate. Examples of the surface conduction electron-emitting device are a device using an SiO2 thin film proposed by Elinson et al., a device using an Au thin film [G. Dittmer: Thin Solid Films, 9, 317 (1972)], a device using In2O3/SnO2 thin film [M. Hartwell and C. G. Fonstad: IEEE Trans. ED Conf., 519 (1975)], and a device using a carbon thin film [Hisashi Araki et al.: Shinkuu (Vacuum), Vol. 26, No. 1, p. 22 (1983)].
As a typical example of these surface conduction electron-emitting devices, the device structure by M. Hartwell is schematically shown in FIG. 2. In FIG. 2, an electroconductive thin film 22 is formed on a substrate 21. The electroconductive thin film 22 is made of a metal oxide thin film or the like sputtered into an H-shaped pattern. The electroconductive thin film 22 undergoes energization operation called energization forming (to be described later) to form an electron-emitting region 24. In FIG. 2, an interval L between device electrodes and W are set to 0.5 to 1 mm and 0.1 mm, respectively.
Another example of the surface conduction electron-emitting device is disclosed in Japanese Laid-Open Patent Application No. 08-321254 or the like. The surface conduction electron-emitting device disclosed in this reference is schematically shown in FIGS. 3A and 3B. FIG. 3A is a schematic plan view of the device, and FIG. 3B is a schematic sectional view taken along the line 3Bxe2x80x943B in FIG. 3A. In FIGS. 3A and 3B, electrodes 2 and 1, electroconductive thin film 3, and electron-emitting region 7 are formed on a substrate 9.
The present inventors have studied a large-area image-forming apparatus having many surface conduction electron-emitting devices arranged on a substrate. An electron source substrate having electron-emitting devices and wires arranged on a substrate can be manufactured by various methods. For example, all device electrodes, wires, and the like are formed by photolithography.
To the contrary, surface conduction electron-emitting devices and an electron source substrate including them can be formed using a printing technique such as screen printing or offset printing. The printing method is suitable for forming a large-area pattern. By forming the device electrodes of surface conduction electron-emitting devices by printing, many surface conduction electron-emitting devices can be easily formed.
Japanese Laid-Open Patent Application No. 8-34110 employs screen printing to form X- and Y-direction wires which are used to drive electron-emitting devices on a rear plate (substrate), and respectively extend in the X and Y-directions, and an insulating layer for insulating the X- and Y-direction wires from each other. An electron source manufacturing method disclosed in this reference will be described with reference to FIG. 11A to FIG. 11F. A plurality of pairs of electrodes 1 and 2 are formed on a substrate 9 (FIG. 11A). An electroconductive paste is applied by screen printing and baked to form wires (y-direction wires) 4 for commonly connecting the electrodes 1 (FIG. 11B). Insulating layers 5 for insulating the wires 4 from wires 6 (to be described later) are formed by applying an insulating paste and baking the paste by screen printing (FIG. 11C). Then, wires (x-direction wires) 6 for commonly connecting the electrodes 2 are formed by applying and baking an electroconductive paste by screen printing (FIG. 11D). An electroconductive film 3 for connecting each pair of electrodes 1 and 2 is formed.(FIG. 11E). An electron-emitting region 7 is formed in each electroconductive film to complete an electron source substrate (FIG. 11F).
According to this method, a low-resistance thick film wire can be manufactured more easily within a shorter operation time per substrate at lower cost, compared to a conventional manufacturing method using photolithography.
In a large-screen, high-resolution plasma display panel (PDP) and a display using a surface conduction electron-emitting device, finer line and space printing is demanded.
According to the present invention, there is provided an electron source substrate comprising a substrate, a Y-direction wire formed on the substrate by a printing method, an X-direction wire formed on the Y-direction wire by the printing method so as to intersect the Y-direction wire, an insulating layer for insulating the Y-direction wire and X-direction wire at the intersection part, and a plurality of electron-emitting devices connected to the X-direction wire and Y-direction wire, wherein at least one of the Y-direction wire and X-direction wire has a surface shape with a surface roughness Ra of not more than 0.3 xcexcm and a surface roughness Rz of not more than 3 xcexcm.
In the present invention, the X- and Y-direction wires are formed by screen printing. Each electron-emitting device has a pair of electrodes, one of the pair of electrodes is connected to the Y-direction wire, and the other electrode is connected to the X-direction wire.
The X-direction wire and Y-direction wire have a surface shape with a surface roughness Ra of not more than 0.2 xcexcm and a surface roughness Rz of not more than 2 xcexcm.
According to the present invention, there is provided an image-forming apparatus comprising an electron source substrate having a plurality of electron-emitting devices, and an image-forming member, the electron source substrate being the above-described electron source substrate.
The present inventors have made extensive studies to find that interlevel insulating errors (short-circuiting between upper and lower wires) at the intersection part between the Y- and X-direction wires and discharge between the face plate and rear plate depend on the surface shapes of the wires.
As a result of various studies, the present inventors have found that the above-described discharge between the rear plate and face plate can be significantly reduced when the Y- or X-direction wire is formed into a surface shape having a surface roughness Ra of 0.3 xcexcm or less and a surface roughness Rz of 3 xcexcm or less. Particularly when the Y- and X-direction wires are formed into a surface shape having a surface roughness Ra of 0.3 xcexcm or less and a surface roughness Rz of 3 xcexcm or less, discharge is further suppressed, and short-circuiting between the X- and Y-direction wires is suppressed.
Note that Ra represents the average roughness along the center line indicating the surface roughness of industrial products, and Rz represents the average roughness of 10 points indicating the surface roughness of industrial products.